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-# phosphor-sel-logger
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+# phosphor-sel-logger
+
+### Overview
+
+The SEL Logger daemon handles all requests to add new IPMI SEL records
+to the journal.  SEL records stored in the journal are identified by
+the standard **MESSAGE\_ID** metadata.  Other metadata fields are used to
+store event-specific information for each record.
+
+### Metadata
+
+SEL records are identified in the journal using the **MESSAGE\_ID** field.
+
+The **MESSAGE\_ID** for SEL records is **"b370836ccf2f4850ac5bee185b77893a"**.
+
+The additional metadata fields for a SEL record are
+
+    IPMI_SEL_RECORD_ID = Two byte unique SEL Record ID
+    IPMI_SEL_RECORD_TYPE = The type of SEL entry (system or OEM)
+                           which determines the definition of the
+                           remaining bytes
+    IPMI_SEL_GENERATOR_ID = The IPMI Generator ID (usually the
+                            IPMB Slave Address) of the requester
+    IPMI_SEL_SENSOR_PATH = D-Bus path of the sensor in the event
+    IPMI_SEL_EVENT_DIR = Direction of the event (assert or deassert)
+    IPMI_SEL_DATA = Raw binary data included in the SEL record
+
+### Interface
+
+The SEL Logger daemon exposes an interface for manually adding System
+and OEM type SEL events, and provides the capability to monitor for
+types of events and log them automatically.
+
+The interface for System type events requires
+
+* A text message to include in the journal entry
+* The sensor path
+* Up to three bytes of SEL data
+* The direction of the event (assertion or deassertion)
+* The generator ID of the requester
+
+The interface for OEM type events requires
+
+* A text message to include in the journal entry
+* Up to thirteen bytes of SEL data (depending on the record type)
+* The record type
+
+The **MESSAGE\_ID** and **IPMI\_SEL\_RECORD\_ID** metadata fields are added by the
+daemon.
+
+### Event Monitoring
+
+The SEL Logger daemon can be configured to watch for specific types of events and
+automatically log SEL records for them.
+
+As an example, the SEL Logger has a "threshold event monitor" which implements a
+D-Bus match for any "PropertiesChanged" event on the
+"xyz.openbmc_project.Sensor.Threshold" interface.  The handler then checks for any
+new threshold events and logs SEL records accordingly.